Electrochemically controlled capillarity to dynamically connect portions of an electrical circuit

ABSTRACT

Embodiments herein describe a capillary containing a eutectic conductive liquid (e.g., EGaIn) and an electrolyte (e.g., NaOH) that is integrated into a printed circuit board (PCB). In one embodiment, the PCB includes a capillary, a negative electrode, a positive electrode, a plurality of insulation layers, and a conductive layer. The capillary extends through the PCB. The capillary includes a side surface forming an annular cylinder. A eutectic conductive liquid and an electrolyte are disposed within an aperture formed by the side surface. An electrode extends through the side surface and contacts at least the eutectic conductive liquid or the electrolyte. The negative electrode is disposed at a first end of the capillary. The positive electrode is disposed at a second end of the capillary. The conductive layer is disposed between two of the plurality of insulation layers. The electrode forms an electrical connection with the conductive layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 16/185,763, filed Nov. 9, 2018. The aforementioned relatedpatent application is herein incorporated by reference in its entirety.

BACKGROUND

The present invention relates to eutectic conductive material, and morespecifically, to disposing a capillary of eutectic conductive liquid ina printed circuit board or flex circuit.

Reconfigurable radiofrequency (RF) electronics are used to enableadaptive, multifunctional radios for wireless sensing andcommunications. Conventionally, reconfigurable components have employedswitched electro-mechanical circuit elements (e.g., diodes andvaractors) on the device to change its RF properties. However, thecircuit elements have a limited number and range of states. To constructmore versatile tunable systems, liquid metals have recently been used ina variety of reconfigurable microwave components—filters frequencyselective surfaces (FSS) and antennas. In these applications, the liquidconductors are pneumatically actuated via pumps or contact pressure tochange RF current paths. While the enhanced control over the conductorlength and location provided by a liquid conductor greatly enhances thetuning range of the devices, the introduction of pumps and microfluidicelements adds to system complexity and requires a closed fluid path,limiting the device topology.

Gallium alloys have attracted attention for reconfigurable electronicsbecause of their liquid state at room temperature and their non-toxicitycompared to mercury. For example, eutectic gallium indium (EGaIn), is aeutectic (lowest melting point composition) mixture of gallium (75%) andindium (25%) with a conductivity of 3.4×10{circumflex over ( )}6 S/m.Although EGaIn reacts with air to form a surface oxide that can stick tosurfaces including the inner walls of capillaries, this adhesion can beavoided by injecting the metal into capillaries pre-filled withelectrolyte. The electrolyte forms a slip layer between the oxide andthe walls of the capillary.

SUMMARY

One embodiment of the present disclosure is a method that includesproviding a capillary comprising a side surface forming an annularcylinder, wherein at least one electrode extends through the sidesurface, inserting the capillary into a through hole of a printedcircuit board (PCB) such that a first portion of the at least oneelectrode is electrically connected to a conductive layer in the PCB,injecting a eutectic conductive liquid and an electrolyte into anaperture formed by the side surface where at least one of the eutecticconductive liquid and the electrolyte contacts a second portion of theat least one electrode, disposing a negative electrode at a first end ofthe capillary and a positive electrode at a second end of the capillaryopposite the first end, and sealing the capillary after the capillary isinserted into the through hole so that the eutectic conductive liquidand the electrolyte are contained within the aperture formed by the sidesurface.

Another embodiment of the present disclosure is a PCB that includes acapillary extending through the PCB where the capillary comprises sidesurface forming an annular cylinder, where a eutectic conductive liquidand an electrolyte are disposed within an aperture formed by the sidesurface, where at least one electrode extends through the side surface,and where a first portion of the at least one electrode contacts atleast one of the eutectic conductive liquid and the electrolyte. The PCBalso includes a negative electrode disposed at a first end of thecapillary, a positive electrode disposed at a second end of thecapillary, a plurality of insulation layers, and a conductive layerdisposed between two of the plurality of insulation layers, wherein asecond portion of the at least one electrode forms an electricalconnection with the conductive layer.

Another embodiment of the present disclosure is a capillary network thatincludes a first capillary, a first negative electrode extending throughthe first capillary, a second capillary in fluid communication with thefirst capillary, a second negative electrode extending through thesecond capillary, a reservoir in fluid communication with both the firstcapillary and the second capillary, a positive electrode extendingthrough the reservoir, and control circuitry configured to control DCvoltages on the first negative electrode, the second negative electrode,and the positive electrode so that a eutectic conductive liquidselectively extends from the reservoir to one of the first capillary andthe second capillary.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates a wireless device with a tuning circuit controlled bya capillary with a eutectic conductive liquid, according to oneembodiment described herein.

FIG. 2 illustrates a flowchart for forming a capillary containing aeutectic conductive liquid in a printed circuit board, according to oneembodiment described herein.

FIG. 3 illustrates drilled holes for forming a capillary, according toone embodiment described herein.

FIGS. 4A and 4B illustrate a cylindrically capillary, according to oneembodiment described herein.

FIG. 5 illustrates inserting electrodes into a side of the capillary,according to one embodiment described herein.

FIG. 6 illustrates a through hole in a printed circuit board, accordingto one embodiment described herein.

FIG. 7 illustrates inserting the capillary in FIG. 5 into the throughhole of the printed circuit board in FIG. 5, according to one embodimentdescribed herein.

FIG. 8 illustrates filling the capillary with electrolyte and a eutecticconducting liquid and mounting electrodes at the ends of the capillary,according to one embodiment described herein.

FIG. 9 illustrates a network of capillaries, according to one embodimentdescribed herein.

FIG. 10 illustrates disposing the network of capillaries in FIG. 9 intoa layer of a printed circuit board, according to one embodimentdescribed herein.

DETAILED DESCRIPTION

Embodiments herein describe a capillary containing a eutectic conductiveliquid (e.g., EGaIn) and an electrolyte (e.g., NaOH) that is integratedinto a printed circuit board (PCB). In one embodiment, the capillary isformed in a through-hole in the PCB and has negative and positiveelectrodes at its respective ends to seal the eutectic conductive liquidand the electrolyte. The capillary further includes one or more wiperelectrodes that extend through a side portion of the capillarycontaining the liquids. The wiper electrodes also make electricalcontact with respective conductive layers in the PCB. Using a DC voltagebetween the negative and positive electrodes, the eutectic conductiveliquid can form electrical connections between the wiper electrodes,which in turn, forms electrical connections between the conductivelayers in the PCB. By controlling which of the wiper electrodes areelectrically coupled via the eutectic conductive liquid, the capillarycan selectively couple different circuitry in, or on, the PCB. Forexample, the capillary can control a tuning circuit for changing theoperating frequency of an antenna. In other examples, the capillary canbe used to isolate circuitry in the case of unauthorized probing by anefarious actor, electrically connect newly added circuitry (e.g., RAMplaced in an expansion slot) to other circuitry in the PCB, and thelike.

FIG. 1 illustrates a wireless device 100 with a tuning circuit 160controlled by a capillary 115 with a eutectic conductive liquid 150,according to one embodiment described herein. The wireless device 100includes an antenna 105 and a PCB 110 but can contain other electricaland mechanical components. For example, the wireless device 100 may be amobile device such as a smart phone, tablet, or laptop. In otherexamples, the wireless device 100 could be a base station in a cellularnetwork (e.g., a 5G wireless network).

The antenna 105 can be separate from the PCB 110 or formed in one of theconductive layers 130 in the PCB 110 (e.g., a patch antenna). In oneembodiment, the antenna 105 is used to perform 5G wirelesscommunication. 5G communication often requires the antenna 105 to tuneover a wide range of operating frequencies. Current electro-mechanicalsolutions are too slow at tuning the antenna 105 or are ill-suited forbeing disposed within a wireless device 100. However, the capillary 115,when used with the tuning circuit 160 can quickly change the operatingfrequency of the antenna 105 to perform 5G communication while beingeasily integrated into the PCB 110.

The PCB 110 includes a plurality of insulation layers 125, which areformed from a non-conductive material, that separate conductive layers130. The conductive layers 130 may be copper foil that is laminated onthe non-conductive material of the insulation layers 125. Chemicaletching can be used to form traces or tracks in the copper foil in theconductive layers 130. Although not shown, vias can be used to passelectrical connections between the conductive layers 130. The PCB 110 isa multi-layered PCB since it includes multiple iterations of insulationlayers 125 and conductive layers 130. Although two lamination layers areshown, the PCB 110 can include any number of layers.

A tuning circuit 160 is electrically connected to the conductive layers130 and to the antenna 105. As discussed below, the location of theeutectic conductive liquid 150 controls the operation of the tuningcircuit 160 which in turn tunes the operating frequency of the antenna105. That is, the eutectic conductive liquid 150 can form an electricalconnection between the conductive layers 130 (or break an electricalconnection between the layers 130) which affects that operatingfrequency of the antenna 105.

The capillary 115 extends through all the layers in the PCB 110. Anegative electrode 135 is disposed on a top side of the capillary 115and a positive electrode 140 is disposed on a bottom side of thecapillary 115. A control circuit 170 (which can be disposed on the PCB110 or external thereof) controls the voltages applied to the negativeelectrodes 135 and the positive electrode 140 in order to control thelength of the eutectic conductive liquid 150 in the capillary 115.Applying a DC voltage between the negative electrode 135 and positiveelectrode 140 controls the length at which the eutectic conductiveliquid 150 extends in the capillary 115. For example, if the controlcircuit 170 applies a negative voltage and the electrodes 135 and 140are reverse biased (e.g., the negative electrode has a higher voltagethan the positive electrode 140), the eutectic liquid 150 pools at thebottom of the capillary 115 near the positive electrode 140. However,when the control circuit 170 applies a positive voltage and theelectrodes 135 and 140 are forward biased (e.g., the negative electrode135 has a lower voltage than the positive electrode 140), the eutecticliquid 150 begins to extend up toward the negative electrode 135. Thelength at which the eutectic liquid 150 extends in the capillary 115 canbe controlled by the voltage difference between the electrodes 135 and140.

Put differently, by applying a DC voltage, the length of the eutecticconductive liquid 150 in the capillary 115 is controlled to eitherextend the liquid 150 from the positive electrode 140 towards thenegative electrode 135 or conversely, to shorten the length of theliquid 150 in a direction towards the positive electrode 140. Oxidationof the leading surface of the eutectic conductive liquid 150 can lowerthe interfacial tension of the liquid 150. The capillary 115 can betuned such that the Laplace pressure of the eutectic conductive liquid150 causes the eutectic conductive liquid 150 to flow upwards in thecapillary 115 and the electrical length increases. Reversing thepolarity of the DC potential electrochemically reduces the oxide layerat the leading surface and returns the eutectic conductive liquid 150 toa state of large tension (a process called “recapillarity”). In theabsence of the oxide layer, Laplace pressure moves the eutecticconductive liquid 150 towards the positive electrode 140, shortening themetal filament and filling the vacated space with the electrolyte 145.

As the positive DC voltage between the electrodes 135 and 140 increases,the eutectic conductive liquid 150 extends up towards the negativeelectrode 135. Eventually, the eutectic liquid 150 reaches the electrode120A, thereby forming an electrical connection between the electrodes120A and 120B. Stated differently, as the eutectic conductive liquid 150rises, it contacts both of the electrodes 120A and 120B forming aconductive path between them. Because the electrodes 120A and 120B alsoare electrically coupled to respective ones of the conductive layers130, the conductive path in the liquid 150 electrically couples theconductive layers 130. Electrically connecting the layers 130 controlsthe tuning circuit 160 to change the operating frequency (e.g., theresonant frequency) of the antenna 105. For example, electricallycoupling the conductive layers 130 may increase or decreases theresistance, capacitance, and/or inductance of the tuning circuit 160which changes the operating frequency of the antenna 105.

In one embodiment, an applied DC voltage can be used to prevent theeutectic liquid 150 from moving when the device is flipped over (as isthe case in a portable electronic device). That is, if the PCB 110 isinverted where the positive electrode 140 is above the negativeelectrode 135 and gravity pulls the eutectic liquid 150 down, theeutectic liquid 150 does not extend done unless a forward biased DCvoltage is applied between the electrodes 135 and 140. In oneembodiment, the control circuit 170 reverse biases the electrodes 135and 140 (when no connection between the electrodes 120 is desired) whichprevents gravity (or the capillary action) from extending the length ofthe eutectic liquid 150 in the capillary 115 regardless of theorientation of the wireless device 100. If the PCB 110 is mounted in afixed device (e.g., a device that would not be rotated duringoperation), then the electrodes may not be reversed biased since gravityholds in the eutectic liquid in the default (non-connected) stateillustrated in FIG. 1.

However, if the device containing the PCB 110 could be orientedarbitrarily during use, in one embodiment the system can use data froman accelerometer in the PCB 110 to determine which end of the capillary115 is down with respect to gravitational forces and treat that side asthe base electrode (e.g., electrode 120B) and establish the DC biasaccordingly. In another embodiment, two capillaries 115 could bedisposed side-by-side in the PCB 110 where the bias circuitry is wiredin opposite directions. While one capillary is forward-biased, the otheris reverse biased, so whichever capillary is right-side-up (relative togravity) has the appropriate forward-bias to extend the eutectic liquid150. The right-side-down capillary, on the other hand, is reverse-biasedand keeps the eutectic liquid 150 in a non-extended state. This approachuses more space on the PCB 110, but does not require the addedcomplexity of reading an accelerometer to determine the orientation.

While FIG. 1 illustrates two electrodes 120 and two layers 130, thecapillary 115 may include three, four, five, etc. electrodes 120 whicheach couple to respective conductive layers 130. As the eutectic liquid150 rises in the capillary 115, the liquid 150 may electrically couplemore of the electrodes 120 which in turn increases (or decreases) theoperating frequency of the antenna 105. When the length of the eutecticliquid 150 in the capillary 115 shrinks (the positive DC voltage isreduced), the liquid 150 may electrically couple fewer of the electrodes120 which in turn decreases (or increases) the operating frequency ofthe antenna 105. Thus, adding more electrodes 120 may increase thegranularity at which the operating frequency of the antenna 105 can becontrolled by the tuning circuit 160.

Moreover, gallium is very corrosive to many/most metals which makesusing an EGaIn material as the liquid 150 difficult without destroyingthe electrodes 120. In one embodiment, the electrdoes 120 are platedwith tantalum which gallium does not corrode. In another embodiment,vapor deposit is used to form a thin film of Au on, e.g., a Cuelectrode. The oxide enhances wetting to the Au and theelectrocapillarity may be controlled to form a layer that the galliumdoes not corrode.

The eutectic conductive liquid 150 can be a gallium alloy (e.g., EGaIn)but is not limited to such. The liquid 150 can be any conductivematerial that is a liquid at room temperature and can be predictivelycontrolled using an applied voltage. However, for simplicity, theremaining discussion assumes the liquid 150 is EGaIn.

Moreover, while FIG. 1 illustrates using an EGaIn capillary 115 to tunean antenna 105, the embodiments herein are not limited to such. Inanother embodiment, the PCB 110 and the capillary 115 may be used in acrypto card application where in response to detecting an unauthorizedprobe trace, the control circuit 170 moves a trace via a new connectionor short circuits the PCB 110 to prevent a nefarious actor from probingthe device. That is, once an intrusion is detected, the control circuit170 can control the capillary 115 to change the connection using theheight of the EGaIn column resulting in a new circuit path or shortcircuiting the card. In another embodiment, the capillary permitscircuit in, or on the PCB to connect to newly added circuitry. Forexample, the PCB 110 may include expansion slots for receiving new RAMmodules, additional CPUs, additional GPUs, and the like. The controlcircuit 170 can use one or more capillaries 115 in the PCB 110 toconnect the newly added hardware elements to circuit or paths already inthe PCB 110. In yet another example, the capillary 115 can be used inself-healing circuits. For example, if a system detects that a signal isstuck in a low or high state due to a broken or shorted connection(e.g., due to a cracked solder joint or Conductive Anodic Filaments(CAF) growth), the system can adjust the bias on the capillary 115 andengage a spare pathway thereby restoring system function.

FIG. 2 illustrates a flowchart of a method 200 for forming a capillarycontaining a eutectic conductive liquid in a PCB, according to oneembodiment described herein. For clarity, the blocks of the method 200are discussed in parallel with FIGS. 3-8 which illustrate various stepsfor forming a capillary in a multi-layered PCB.

At block 205, a machine or technician drills a hole in a sheet ofsilicone such that the hole does not extend through the sheet. Forexample, FIG. 3 illustrates drilled holes 305 for forming a capillary,according to one embodiment described herein. The holes 305 are formedin a sheet 300 of silicone which, in one embodiment, has a thickness (T)that is slightly greater (e.g., 1-10% greater) than the thickness of thePCB in which the capillary is going to be formed. In one embodiment, thethickness of the sheet 300 (and the corresponding PCB) may range from 50mils to 300 mils, which varies depending on the number of layers in thePCB.

The width (W) of the holes 305 define the space in which the EGaIn andelectrolyte will be disposed when the capillary is formed in the PCB.The width can vary, but should be selected so that a capillary actioncan be used to extend or shrink the EGaIn within the hole 305 asdescribed above.

Although silicone is described, this is only one suitable material. Inone embodiment, any material can be used to form the sides of thecapillary as long as the material permits the capillary action describedabove. Other suitable materials may include rubber orpolytetrafluoroethylene-based materials.

At block 210, a machine or technician punches out a capillary containingthe drilled hole. For example, a region around each of the holes 305illustrated in FIG. 3 can be punched out to form respective capillaries,which in this example, have a cylindrical shape.

FIGS. 4A and 4B illustrate a cylindrically capillary, according to oneembodiment described herein. Specifically, FIG. 4A illustrates a crosssection of a capillary 400 that can be formed by punching out a regionaround the holes 305 formed in the sheet 300 in FIG. 3. FIG. 4Billustrates a plan view of the capillary 400. Because the hole 305 doesnot extend through the capillary 400, the capillary 400 includes abottom surface but no top surface. An annular cylindrical side surfaceof the capillary 400 extends around the hole 305.

At block 215, a machine or technician inserts electrodes into a side ofthe capillary that extend into the hole. FIG. 5 illustrates insertingelectrodes 120 into a side surface 505 of the capillary 400 illustratedin FIG. 4, according to one embodiment described herein. The siliconematerial of the capillary 400 is self-sealing so that inserting theelectrodes 120A and 120B through the side surface 505 does not create apath through which the EGaIn and electrolyte liquid (which are insertedinto the capillary 400 in later steps) can leak.

The electrodes 120 (also referred to as wiper electrodes) each have afirst portion 510 that extends into the hole formed by the side surface505 and a second portion 515 that remains on the outside of thecapillary 400. The first portions 510 extend far enough into the hole sothat when the EGaIn liquid extends through the hole, the EGaIn liquidcontacts the first portions 510 of the electrodes 120. Thus, the EGaInliquid can form electrically connections between the electrodes 120.However, when the first portion 510 contacts the electrolyte, theelectrode 120 is insulated from the other electrodes 120

In one embodiment, the electrodes 120 are inserted into the side surface505 with a spacing that correspond to a spacing of the conductive layersin the PCB. For example, if the layers of the PCB are spaced apart 5mils, the electrodes 120 may be spaced apart by 5 mils along the sidesurface 505. Thus, when the capillary 400 is placed in the PCB asdiscussed below, the second portions 515 can be aligned with, and makeelectrical connections to, respective conductive layers in the PCB.

At block 220, a machine or technician inserts the capillary into athrough hole in a multi-layered PCB so that the electrodes contactconductive layers in the PCB. FIG. 6 illustrates a through hole 605 in aPCB 600, according to one embodiment described herein. Specifically,FIG. 6 illustrates a cross section of the PCB 600. In one embodiment,the through hole 605 is a plated through hole (PTH). The through hole605 may have a diameter or width that corresponds to the diameter of theside surface 505 of the capillary 400 so that the capillary 400 can fitinside the through hole 605.

The PCB 600 also includes a landing 610A disposed around a top of thethrough hole 605 and a landing 610B disposed around a bottom of thethrough hole 605. The landings 610 can form a bond pad or bondingsurface around the through hole 605 which can be used to electricallycouple the capillary to control logic in later processing steps.

FIG. 7 illustrates inserting the capillary 400 in FIG. 5 into thethrough hole 605 of the PCB 600 in FIG. 5, according to one embodimentdescribed herein. As shown, the position of the capillary 400 relativeto the PCB 600 is controlled so that the electrodes 120A and 120B alignto respective conductive surfaces 130A and 130B to form electricalconnections therebetween.

At block 225, a machine or technician injects a eutectic conductiveliquid (e.g., EGaIn) and an electrolyte (e.g., NaOH) into the drilledhole of the capillary 400. For example, the technician may use a needleor pipet to insert a desired ratio of EGaIn and electrolyte into thecapillary. In one embodiment, the technician may fill the drilled holein the capillary completely with a ratio of the EGaIn and electrolyte.However, in another embodiment, a portion of the capillary may includean air pocket—i.e., the capillary is not completely filled.

At block 230, a machine or technician places negative and positiveelectrodes at respective ends of the capillary. FIG. 8 illustratesmounting the negative electrode 135 and the positive electrode 140 atthe ends of the capillary 400, according to one embodiment describedherein. As shown, the negative electrode 135 is disposed over the sidesurface of the capillary 400. The positive electrode 140 is pushedthrough the bottom of the capillary 400 so that at least a portion ofthe positive electrode 140 extends into the hole and contacts the liquid150.

At block 235, a machine or technician seals the respective ends of thecapillary 400 so that the electrolyte 145 and the eutectic conductiveliquid 150 cannot escape the capillary 400 regardless of the orientationof the PCB 600. To seal the top end of the capillary 400 andelectrically connect the negative electrode 135, solder is 805 is formedaround the capillary 400 and the negative electrode 135. In oneembodiment, the solder 805 provides a dual purpose by holding thenegative electrode 135 in place to seal the top of the capillary 400(and prevent the electrolyte 145 and conductive liquid 150 fromescaping) as well as electrically connecting the negative electrode tothe landing 610A. Although not shown, the landing 610A is electricallyconnected to control circuitry which drives a DC voltage onto thenegative electrode 135.

In another embodiment, rather than resting the negative electrode 135 ontop of the side surface of the capillary 400, the diameter of thenegative electrode 135 may be approximately the same as the diameter ofthe hole in the capillary 400 so that the negative electrode 135 can bepressed down into the hole. This may improve the seal the negativeelectrode 135 forms at the top of the capillary 400. Although a portionof the negative electrode 135 is in the hole, the electrode 135 cannonetheless be solder bonded or wire bonded to the landing 610A.

Because the bottom surface of the capillary is not open like the topsurface, the positive electrode 140 is pushed through the bottom of thecapillary 400. Like when inserting the electrodes 120 into the side ofthe capillary 400, inserting the positive electrode 140 through siliconemay also be self-sealing. However, if not, the bottom surface cannonetheless be sealed by soldering the positive electrode 140 to thelanding 610B. The solder 805 also electrically connects the positiveelectrode 140 to the landing 610B which is in turn electricallyconnected to the control circuitry. In this manner, the controlcircuitry can drive DC voltages onto the negative electrode 135 and thepositive electrode 140 to control the length at which the liquid 150extends through the capillary 400.

While FIG. 8 illustrates two electrodes 120 and two conductive layers130, the capillary 400 can include any number of electrodes 120 andconductive layers 130. For example, when using the capillary inconjunction with a tuning circuit, the capillary 400 may include five,six, seven, etc. electrodes 120. In another example, the capillary 400may include only one electrode 120 inserted in its side. In thisexample, the positive electrode 140 could be dual purposed to apply a DCvoltage to control the length of the eutectic liquid 150 as well as anAC signal which can be transmitted, via the liquid 150 to the wiperelectrode 120.

FIG. 9 illustrates a network of capillaries 905, according to oneembodiment described herein. That is, FIG. 9 illustrates a capillarynetwork 900 that includes a first capillary 905A, a second capillary905B, and a reservoir 920. FIG. 9 provides a top view of the capillaries905 which may be disposed horizontally in (or on) a PCB in contrast toFIGS. 1 and 8 which illustrate a capillary that extends vertically in aPCB. In this example, the first capillary 905A and the second capillary905 extend along different axes—e.g., the first capillary 905A isperpendicular to the second capillary 905 and form a T-junction alongwith the reservoir 920.

The network 900 includes two negative electrodes 135A and 135B and apositive electrode 140. When the DC voltage is reversed biased betweenboth of the negative electrodes 135A and 135B and the positive electrode140, the eutectic conductive liquid 150 remains in the reservoir 920proximate to the positive electrode 140. However, the control circuitcan forward bias the voltage between one of the negative electrodes 135and the positive electrode 140 to establish an electrical path betweenthe positive electrode 140 and one of the connection electrodes 910.

For example, in a first mode of operation, the control circuit mayforward bias the voltages between the negative electrode 135A and thepositive electrode 140 while maintaining the reverse bias between thenegative electrode 135B and the positive electrode 140. That is, thenegative electrode 135A has a lower voltage than the positive electrode140, while the negative electrode 135B has a higher voltage than thepositive electrode 140. As a result, the EGaIn liquid extends throughthe capillary 905A but not the capillary 905B. As the positive biasbetween the negative electrode 135A and the positive electrode 140increases, eventually the EGaIn forms an electrical connection betweenthe positive electrode 140 and the connection electrode 910A.

In a second mode of operation, the control circuit may forward bias thevoltages between the negative electrode 135B and the positive electrode140 while maintaining the reverse bias between the negative electrode135A and the positive electrode 140. That is, the negative electrode135B has a lower voltage than the positive electrode 140, while thenegative electrode 135A has a higher voltage than the positive electrode140. As a result, the EGaIn liquid extends through the capillary 905Bbut not the capillary 905A. As the positive bias between the negativeelectrode 135B and the positive electrode 140 increases, eventually theEGaIn forms an electrical connection between the positive electrode 140and the connection electrode 910B.

The capillary network 900 can be used in a variety of circuits. Forexample, the network 900 may be used to select pull-up or pull-downtermination for a signal, select a path with more or less delay fortiming optimization, or tune a resonator by adding or removinginductance or capacitance depending on which connection electrode 910 iselectrically coupled to the positive electrode 140. Further, althoughtwo capillaries 905 are in the network 900, the network 900 couldinclude additional capillaries with a corresponding connectionelectrodes 910 and negative electrodes 135.

The connection electrodes 910, negative electrodes 135, and the positiveelectrode 140 can be coupled to an underlying conductive layer viarespective pads 915. For example, the capillary network 900 may beformed in an internal layer of a PCB where the pads 915 are part of aconductive layer in the PCB. In another embodiment, the capillarynetwork 900 may be mounted on an outer layer of the PCB where the pads915 are bond pads that can be soldered to the electrodes 910, 135, and140.

The capillaries 905 can be formed using a similar process as explainedabove except that the capillaries 905 are not disposed in through holesin the PCB. Rather, the capillary network can be formed, filled with theliquid material, and sealed before being disposed in or on the PCB. Whendisposing the capillary network 900 on the PCB, soldering the electrodes910, 135, and 140 onto the pads 915 in the PCB can hold the network 900in place.

FIG. 10 illustrates disposing the network 900 of capillaries in FIG. 9into a layer of a PCB, according to one embodiment described herein. Inone embodiment, the capillary network 900 is mounted onto the PCB 1000after the conductive layer 1010A, the insulation layer 1005A, and theconductive layer 1010B has been formed but before the insulation layer1005B, conductive layer 1010C, insulation layer 1005C, and theconductive layer 1010D have been formed.

In one embodiment, the conductive layer 1010B may be patterned to formthe pads 915 illustrated in FIG. 9 and solder 1015 can be used toconnect the various electrodes in the capillary network 900 to the pads915 in the layer 1010B. Once connected, the insulation layer 1005B canbe formed around and on the capillary network 900 to encapsulate thecapillary network 900 in an internal layer in the PCB 1000. Theadditional conductive layers 1010C and 1010D and the insulation layer1005C can then be formed. Thus, the capillary network 900 is hidden fromanyone viewing the PCB 1000. However, as mentioned above, rather thandisposing the capillary network 900 in the PCB 1000, in anotherembodiment, the network 900 can be disposed on the outer layers of thePCB—i.e., the conductive layers 1010A and 1010D.

As used herein and in the claims, “at least one of A and B” covers theoptions of only A, only B, and the combination of A and B.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

In the preceding, reference is made to embodiments presented in thisdisclosure. However, the scope of the present disclosure is not limitedto specific described embodiments. Instead, any combination of thefeatures and elements described above, whether related to differentembodiments or not, is contemplated to implement and practicecontemplated embodiments. Furthermore, although embodiments disclosedherein may achieve advantages over other possible solutions or over theprior art, whether or not a particular advantage is achieved by a givenembodiment is not limiting of the scope of the present disclosure. Thus,the aspects, features, embodiments and advantages described above aremerely illustrative and are not considered elements or limitations ofthe appended claims except where explicitly recited in a claim(s).Likewise, reference to “the invention” shall not be construed as ageneralization of any inventive subject matter disclosed herein andshall not be considered to be an element or limitation of the appendedclaims except where explicitly recited in a claim(s).

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A printed circuit board (PCB), comprising: acapillary extending through the PCB, wherein the capillary comprises aside surface forming an annular cylinder, wherein a eutectic conductiveliquid and an electrolyte are disposed within an aperture formed by theside surface, wherein at least one electrode extends through the sidesurface, and wherein a first portion of the at least one electrodecontacts at least one of the eutectic conductive liquid or theelectrolyte; a negative electrode disposed at a first end of thecapillary; a positive electrode disposed at a second end of thecapillary; a plurality of insulation layers; and a conductive layerdisposed between two of the plurality of insulation layers, wherein asecond portion of the at least one electrode forms an electricalconnection with the conductive layer.
 2. The PCB of claim 1, furthercomprising: a first landing disposed on a first outer surface of thePCB, wherein the first landing is connected via solder to the negativeelectrode; and a second landing disposed on a second outer surface ofthe PCB, wherein the second landing is connected via solder to thepositive electrode.
 3. The PCB of claim 2, wherein the first and secondlandings surround the side surface of the capillary.
 4. The PCB of claim1, wherein a plurality of electrodes extends through the side surface,wherein first portions of the plurality of electrodes contact at leastone of the eutectic conductive liquid or the electrolyte and secondportions of the plurality of electrodes form electrical connections witha plurality of conductive layers in the PCB.
 5. The PCB of claim 4,wherein each of the plurality of insulation layers is disposed between apair of the plurality of conductive layers.
 6. A capillary network,comprising: a first capillary; a first negative electrode extendingthrough the first capillary; a second capillary in fluid communicationwith the first capillary; a second negative electrode extending throughthe second capillary; a reservoir in fluid communication with both thefirst capillary and the second capillary; a positive electrode extendingthrough the reservoir; and control circuitry configured to control DCvoltages on the first negative electrode, the second negative electrode,and the positive electrode so that a eutectic conductive liquidselectively extends from the reservoir to one of the first capillary andthe second capillary.
 7. The capillary network of claim 6, wherein thefirst capillary extends along a different axis than the secondcapillary.
 8. The capillary network of claim 7, wherein the firstcapillary, the second capillary, and the reservoir form a T-junction. 9.The capillary network of claim 6, further comprising: a first connectionelectrode extending through the first capillary; and a second connectionelectrode extending through the second capillary, wherein the controlcircuitry is configured to control the DC voltages to selectively form,using the eutectic conductive liquid, one of a first electrical pathbetween the positive electrode and the first connection electrode and asecond electrical path between the positive electrode and the secondconnection electrode.
 10. The capillary network of claim 9, furthercomprising: a printed circuit board (PCB) comprising a plurality ofpads, wherein the first negative electrode, the second negativeelectrode, the positive electrode, the first connection electrode, andthe second connection electrode are coupled to respective ones of theplurality of pads.
 11. The capillary network of claim 10, wherein thefirst capillary, the second capillary, and the reservoir are mounted onan outer surface of the PCB.
 12. The capillary network of claim 10,wherein the plurality of pads is in a first conductive layer in the PCB,wherein the first capillary, the second capillary, and the reservoir aredisposed in an internal layer of the PCB between the first conductivelayer and a second conductive layer.